This invention relates to a method and apparatus for precision metering of high viscosity materials. The invention utilizes known gear pump technology with novel material feeding concepts to achieve extremely accurate delivery of very high viscosity materials at widely varying predetermined pressures. As used in this application, the term "high viscosity" means viscosity on the order of 3,000 centipoise or greater. Such materials are technically considered liquids, since they will assume the shape of the container within which they reside, but are so viscous that they will support significant weight. These factors are put to use in the practice of the present invention.
Gear pumps are well-known as devices which can meter and deliver extremely precise volumes of materials across a wide range of viscosities, temperatures and pressures. Properly maintained gear pumps have extremely long duty cycles, operate in harsh environments and are inherently resistant to process variations such as pulsation and surging. The robust nature of gear pumps make them ideal for metering precise quantities of materials at high pressures. Other pumps which are used for similar applications include piston, diaphragm, peristaltic and moyno pumps.
Gear pumps in the presence of low or no inlet pressure have heretofore not been usable with materials having extremely high viscosity, because the materials are too viscous to flow into the gear pump inlet. Auxiliary pumps used to create inlet pressure increase cost, complexity and introduce additional processing variables which often present unanticipated and unpredictable results. This invention relates to a modified gear pump which will feed itself extremely viscous materials while maintaining the precision and simplicity for which gear pumps are known. The metering gears and feeding means are driven in unison by the same motor, thus automatically matching feed and delivery rates.